1. Field of the Invention
This invention relates in general to a temperature indicating device and, more particularly, to a pop-up temperature indicator for use in cooking foods.
2. Prior Art
Pop-up thermometers have been used for measuring internal temperatures when cooking meat, poultry and the like. Such thermometers typically include a barrel-shaped housing and an indicator rod retained in the barrel by a fusible material. When a predetermined temperature is reached, the fusible material softens, releasing the indicator rod from the barrel to provide a visual indication that the product is fully cooked. With the pop-up thermometer, a consumer may safely prepare meat or poultry without overcooking the product. U.S. Pat. No. 4,748,931 discloses one such pop-up thermometer.
To ensure the thermometer provides a reliable, accurate indication of the internal temperature of the product, the fusible material must securely retain the indicator rod within the housing until the thermometer has been heated to a predetermined temperature. If the indicator rod is allowed to creep slightly out of the housing during the cooking or heating process, a user may mistakenly interpret the thermometer as indicating that the product has been sufficiently cooked. During shipment of the temperature indicating devices, the indicator rod may creep from the housing if the devices are inadvertently heated. Even if the rod moves only a minimal distance relative to the housing, the thermometer may be rendered unusable.
Various factors may cause creep or premature extension of the indicator rod. During manufacture, an insufficient amount of fusible material may be added to the housing. For example, when the fusible material is supplied in pellet form, pellet breakage may result in pellet fragments being inserted in some thermometer housings. The traditional alloy materials used to retain the indicator rod in the housing are increasingly being replaced by organic materials. The organic materials generally have a lesser strength than the alloy materials, increasing the risk that the indicator rod will become displaced from the thermometer housing.
This invention provides a new and improved pop-up thermometer in which the indicator rod is securely retained in the thermometer housing until a predetermined temperature is attained. Premature creep or displacement of the indicator rod is avoided even when the thermometer is exposed to elevated temperatures during shipment or storage of the device, uses an organic material to retain the indicator rod in the housing, includes less than the desired amount of fusible material, etc. Even under adverse conditions, with the present invention the indicator rod is securely retained within the housing to provide a highly accurate, reliable thermometer for indicating when meat, poultry or other products have been heated to a predetermined internal temperature.